[PATCH] usb: core: improve handling of hubs with no ports

[Alan Stern]

On Wed, Feb 23, 2022 at 01:26:23PM +0100, Heiner Kallweit wrote:
> On 23.02.2022 03:10, Alan Stern wrote:
> > On Tue, Feb 22, 2022 at 10:13:09PM +0100, Heiner Kallweit wrote:
> >>
> >> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> >> index 83b5aff25..e3f40d1f4 100644
> >> --- a/drivers/usb/core/hub.c
> >> +++ b/drivers/usb/core/hub.c
> >> @@ -1423,9 +1423,8 @@ static int hub_configure(struct usb_hub *hub,
> >>  		ret = -ENODEV;
> >>  		goto fail;
> >>  	} else if (hub->descriptor->bNbrPorts == 0) {
> >> -		message = "hub doesn't have any ports!";
> >> -		ret = -ENODEV;
> >> -		goto fail;
> >> +		dev_info(hub_dev, "hub has no ports, exiting\n");
> >> +		return -ENODEV;
> >>  	}
> >>  
> >>  	/*
> > 
> > How about instead changing xhci-hcd so that it doesn't try to register 
> > a USB-3 root hub if the controller doesn't have any USB-3 ports?  I 
> > think that would make more sense.
> > 
> Right, this would be better. I checked and it seems to be a little bit
> bigger endeavor. If I let register_root_hub() fail, then this removes
> the USB3 bus/host (shared hcd), but also the USB2 bus/host.
> It took an additional change to xhci_plat_probe() to make it work on my
> system. Not sure what the impact could be on systems not using
> xhci_plat_probe(). Users may face the same issue like me, and having
> a USB3 hub with no ports may remove also the USB2 bus/host.

Don't change register_root_hub().  Just change xhci_plat_probe(); make 
it skip the second call to usb_add_hcd() if there are no USB-3 ports.

Alan Stern

> What I can do: submit my patches as RFC, then there's a better basis
> for a discussion.
> 
> > Alan Stern
> 
> Heiner